1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to an improved belt type fusing device to fuse a developer image onto a recording medium and an image forming apparatus having the same.
2. Description of the Related Art
In general, an image forming apparatus using an electrophotographic process, such as a printer, a photocopier, and a multifunction peripheral, has a fusing device to semi-permanently fuse a developer image transferred to a recording medium by a transfer device onto the recording medium by heating and pressing the developer image. Such a fusing device includes a roller type fusing device and a belt type fusing device.
The main technical requirements for the fusing device are heating performance and fusing performance. In order to achieve high speed heating performance, a heater should decrease a heat capacity. Main factors affecting toner fusing performance are temperature, pressure, and nip width. If the fusing temperature is higher within a range from a cold offset to a hot offset, the fusing performance can be better, and also if the pressure is higher and the nip width is larger, a better fusing performance can be achieved.
FIG. 1 is a view illustrating a conventional roller type fusing device. As illustrated in FIG. 1, the conventional roller type fusing device includes a pressure roller 10 and a heating roller 20 which are rotated in close contact with each other, and a heating member 30 disposed in the heating roller 20. In this fusing device, the heating member 30 has a high heat capacity, and since the fusing device is designed to heat the entire heating roller 20, a long time is required to heat the heating roller 20. Also, since a nip N is formed on a contact surface between the pressure roller 10 and the heating roller 20, the width of the nip P is narrow.
FIG. 2 is a view illustrating a conventional belt type fusing device suggested for the purpose of enhancing a heating temperature. The fusing device of FIG. 2 includes a pressure roller 10, a fusing belt 40 rotating with a rotational force received from the pressure roller 10, a guide member 50 disposed in the fusing belt 40 to guide a rotational movement of the fusing belt 40, and a heating member 60 disposed on the guide member 50 to heat a nip N of the fusing belt 40.
The belt type fusing device described above has a low heat capacity of the heating member 60 and employs a localized heating method of heating only the nip N. Compared to the roller type fusing device of FIG. 1, the belt type fusing device can shorten a time required to heat and broaden the width of the nip N. However, since the heating member 60 is disposed on the nip N and thus is subjected to a pressure from the pressure roller 10, the pressure of the pressure roller 10 is limited below an endurance strength of the heating member 60. Therefore, the pressure at the nip N is lower than expected and thus good fusing performance cannot be achieved due to an insufficient level of pressure. Also, if the pressure at the nip N is increased in order to enhance the fusing performance, the heating member 60 may be damaged due to pressure and thermal deformation.